Heating system



De@ 5 1944- H. J. DE N. MccoLLuM 2,364,458

HEATING SYSTEM Filed Oct. 5, 1941 Wm.. NN. QM'.

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Patented Dec. 5, 1944 UNITED STATES PATENT OFFICE HEATING SYSTEM HenryJ. De N. McCollum, Chicago, lll.

Application October 3, 1941, Serial No. 413,463

21 Claims. (Cl. 237-123) My invention relates generally to heating sysltems, and more particularly to an internalffcombustion heating systemfor use in heating airplanes and the like.

It is an object of my invention to provide an internal combustionheating system which has a large heating output, which is self-containedand light in weight, and which occupies a minimum of space.

It is another object of my invention to provide an internal combustionheating system which is operated by power lderived from the flow of acurrent of air through the heating unit.

Itis another object to provide an internal combustion heating systemwhich will discontinue the supply of fuel to the heating system shouldthe current of air flowing past the heating unit be interrupted, so thatthere is no danger of overheating a part of the system.

It is a further object to provide a heating system for airplanes whichwill be conditioned for operation incidental to opening a valve topermit air to flow through the heating system to the airplane cabin.

It is a further object to provide an internal combustion heating systemwhich is simple and rugged in construction and reliable in operation.

It is a further object to provide an internal combustion heating systemwhich will not become overheated at low rates of flow of air to beheated.

It is a further object to provide an internal combustion heating system,for use in heating airplanes and the like, which presents no appreciablere hazard.

Other objects will appear from the following description, referencebeing had tothe accompanying drawing in which:

Fig. 1 is a diagrammatic cross-sectional view of a heating systemillustrating one embodiment of my invention; and

Fig. 2 is a diagrammatical cross-sectional view, similar to Fig. 1,showing a second embodiment of my invention.

The embodiment, of my improved heating system shown in Fig. 1 isdesigned and constructed to be used in heating an airplane which doesnot have a. supercharged cabin. The heating system may be installed inthe fuselage or in the engine nacelle of the airplane. Air from asuitable source of air under pressure flows past the heat-y ing unit ID,through an air turbine I2 which operates a positive displacement blower'I4 to supply combusti-ble mixture to the heating unit Il), and throughan outlet conduit I6 to the cabin passenger compartment ofthe airplane.The conduit I 6 may be branched so that part of the heated air may beused to heat other compartments of the airplane, such as the gunner-scompartment when the heating system is used to heat a bomber.

The source of air under pressure is illustrated as being a ram i3positioned adjacent the outer surface of the airplane wall i9, openinginto the slip stream of the airplane or the slip stream of the airplanepropeller, whichever is more effective to produce a positive pressure inthe ram it. An air supply conduit 20 conveys the air under pressure tothe inlet of the casing 22 which encloses the heating unit l0, which maybe of the construction disclosed and claimed in my copending applicationSerial No. 378,262, filed February 10, 1941. The outlet of the casing 22is connected to a turbine housing 2t which encloses a suitable airturbine rotor 26. The rotor 26 may be a Sirocco" type fan rotor havingits blades shaped to render it eective as an air turbine. Heated airfrom the outlet 28 of the turbine casing 24 passes to the airplane cabinthrough a conduit I6. i

The positive displacement blower i4, which may be of the Roots'orcycloidal type, is mounted upon the same shaft 30 as the air turbinerotor 26. The blower it draws combustible mixture from a suitablecarburetor 32, illustrated as a balanced carburetor, and forces it tothe heating unit I0, where it is ignited and burned.

The carburetor 32 receives liquid fuel from a, fuel supply 34 and mixesit with air to form a combustible mixture. While the carburetor 32 mayreceive air from any suitable source, it is shown as receiving airthrough a duct 36 having its inlet opening positioned in the air supplyconduit 2D of the heating system. This arrangement of the carburetor airsupply causes the carburetor to operate at above atmospheric pressure,thereby reducing the load upon the positive displacement blower I4 andincreasing the eiciency of the system. Also, the location of thecarburetor air inlet in the heating system air supply conduit 20substantially removes the re hazard of the system, in that it preventscombustible mixture and/or liquid fuel from escaping from the carburetorair inlet and accumulating in the compartment in which the heatingsystem is located.

The heating unit Ill, which is described and claimed in my aforesaidco-pending application Serial No. 378,262, led February 10, 1941,comprises a suitable combustion chamber housing 38 which is suppliedwith combustible mixture through a duct 48' connected with the outletoi' the blower I4. The combustible mixture within the combustion chamberis ignited by a suitable electrical igniter 42 and burned. The hot gasesof combustion therefrom pass into a heat exchanger shell 44, and throughthe heat exchanger shell to an exhaust pipe 48 which discharges themoverboard at a point adjacent the outer surface of the plane. A hood 48may be placed over the discharge end of the exhaust pipe and positionedso that it faces away from the direction of ilight of the airplane sothat the motion of the airplane creates a partial vacuum which aids incausing combustible mixture to ilow from the carburetor through theheating system. A plurality of radially spaced longitudinal fins 48 aresecured to the outside of the shell 44 to conduct heat to the airflowing through the system.

The electric igniter 42 may suitably be of the resistance type and maycomprise a. coil of nichrome wire heated to incandescence by-the passageof current therethrough. It is supplied with electric current from anyconvenient source, such as a grounded battery 58.

When the igniter 42 is energized, current ows from the hot side of thebattery 50, through a control switch 52, 54, which may be opened andclosed incidental to stopping and starting the operation of the system,through a thermal switch 58, 5l which is located to be responsive to thetemperature of the heating unit I and which is open when hot and closedwhen cold. to the igniter 42 and from there to the ground. The thermalswitch may comprise a bimetal 58 which warps away from a stationarycontact 51 upon the the occurrence of combustion. In order to avoidarcing between the bimetal 58 and the contact l, it is preferable thatthe bimetal 58 have a snap action.

The flow of air past the heating unit I0 may be controlled by a valve ora damper 58 which may be operated manually. or operated by a suitablethermostatic control responsive to the temperature of the cabin of theairplane. While the valve 58 is illustrated as being in the heatingsystem air supply conduit 20, it may be located at any other suitablepoint, such as in the heated air outlet conduit I8.

The control switch 52, 54 may comprise a resilient switch arm 52 and astationary contact 54. In order to operate the switch 54 so that currentmay flow to the igniter 42 when and only when the system is operating, alever arm 80 is mounted upon the same shaft as the valve 58 and isangularly positioned to engage the lower end of the resilient switch arm52 when the valve 58 is in a position to prevent the flow of air throughthe heating system, thereby opening the switch 52, 54 and preventing theenergization of the igniter 42. When the Valve 58 is opened sufficientlyto permit air to :dow through the heating system and cause it tooperate, the arm 8U is withdrawn from the switch arm 52 so that theigniter 42 may be energized.

Assuming that the airplane is in motion, opening of the valve 58 willpermit the heating system to operate. Air will then ilow from the ramI8, past the heating unit I 0, through the air turbine I2, through theconduit I8, to the space to be heated. The moving air rotates the rotor28 of the air turbine I2 and actuates the positive displacement blowerI4, which draws a combustible mixture of fuel and air from thecarburetor 32 and forces it through the conduit 48 to the heating unitI0. Opening of the valve 88 closes the control switch 82, 84 andelectric current from the grounded battery passes through the switches82, 84, and 8l, 51 to the igniter 42. The ,combustible mixture isignited by the igniter 42 and the hot gases of combustion therefrom passthrough the heat exchanger shell 44 and through the exhaust pipe 48 tothe outside of theA airplane. The heat of combustion heats the bimetal58 and causes it to warp away from the contact 51 and decnergize theigniter. The heat of combustion also heats the longitudinally disposedfins 49 which transfer heat to the air passing to the cabin.

The rate of flow of air through the heating system may be controlled byadjusting the valve 58, resulting in the control of the amount of heatedair supplied to the airplane cabin. As the valve 58 is closed to reducethe rate of iiow of air through the heating system, the rate of flow ofair through the air turbine I2 is also reduced. The turbine rotor 28then revolves more slowly and the amount of combustible mixture suppliedby the blower I4 to the heating unit I8 is reduced. The operation of theheating system is thus very stable and the heating unit I0 cannot becomeoverheated when the system is operated at a fraction of its capacity.When it is desired to discontinue the operation of the heating systemthe valve 58 may be closed, stopping the ow of air through the heatingsystem and thereby discontinuing the supply of combustible mixture tothe heating system I0. Closing of the valve 58 also causes the lever 80to engage the lower end of the resilient switch arm 52 and open theignition circuit 52, 54 to prevent current from flowing through theigniter.

Fig. 2 shows an embodiment of my improved heating system which may beused to heat an airplane having a supercharged cabin and which will notinterfere with the normal operation of the cabin supercharger. Partswhich are similar to parts shown in Fig. 1 and which have been describedin connection therewith are similarly numbered.

The cabin supercharger 8| is used as a source of air under pressure foroperating the heating system. The air inlet conduit 20 of the heatingSystem leads from the outlet of the cabin supercharger to the inlet ofthe casing 22 which encloses the heating unit I0.

A by-pass conduit 82 is provided to conduct air directly from the outletof the supercharger 8| to the conduit I8, so that air passing to thecabin need not pass through the casing 22 and air turbine I2.

A valve 84 is provided to control the operation of the heating system.This valve 84 may be positioned to'close either the air turbine outlet28 or the by-pass conduit 82, or it may be placed in an intermediateposition. When the outlet 28 of the air turbine is closed, the heatingsystem is inoperative and all of the air passing from the supercharger8| to the airplane cabin passes through the by-pass 82. When the by-pass82 is closed, all of the air passing to the airplane cabin is used tooperate the heating system and is heated thereby, so that the heatingsystem operates at its maximum heat output. When the valve 84 is in anintermediate position, part of the air from the cabin supercharger 8|passes through the by-pass and is not heated, and the rest of the airoperates the heating system at a fraction of its capacity and becomesheated.

The valve may be controlled manually or may be controlled by a suitablethermostatic conltrol responsive to the cabin temperature. The valve andconduit arrangement' shown may be replaced by any other suitablearrangement for controlling the relative amounts of heated and unheatedair passing from the cabin supercharger 6I to the cabin.

The flow of air through the air turbine I2 rotates the rotor 26 whichdrives the positive displacement blower I4. The operation oi the blowerI4 causes combustible mixture from a balanced carburetor 32 to ilow theheating system. The carburetor 32 may have its outlet connected with theinlet of the blower I4, as shown in Fig. 1, or it may have its air inletconnected with the outlet of the blower I4 by a. duct 61, so that theblower I4 supplies air under pressure to the inlet of the carburetor, asshown in Fig.V 2. The balanced carburetor 32 receives liquid fuel from asuitable fuel supply 34. This fuel supply 34 must deliver fuel to thecarburetor 32 at a. positive pressure in excess of the highest pressurewhich Will be created in the duct 61 by the blower I4 during theoperation of the heating system.

Air may be supplied to the inlet of the blower I4 from a three-way valve66. The three-way valve 66 may be positioned either to supply airdirectly from the atmosphere to the inlet of the blower I4, or to supplyair under pressure from the outlet of the supercharger 6I, through theduct 36, to the inlet of the blower I4.

An electrical igniter 42, which may be of the type described inconnection with Fig. l, is provided with an electrical circuit whichreceives electric current from a suitable source, illustrated as agrounded battery 50. In series with the igniter 42 and the battery 50 isa. pressure responsive switch assembly 68, 10, 12, which is responsiveto the pressure created by the operation of the blower I4 and which isclosed when and only when the pressure created by the blower I4 issufficiently high to cause enough 'combustible mixture to ow to theheating unit l to support combustion. The switch 68, 10, 12 isillustrated as comprising a stationary contact 68 and a resilient switcharm 10 biased away from the contact 68. The interior of a pressureresponsive expanding bellows 12 is in communication with the fluidflowing from the blower I4 to the heating unit Iii. The bellows 12 isillustrated as having one end secured to the heating unit combustiblemixture supply duct 40 and having its interior in communication with theinterior of the duct 40. The unsecured end of the bellows 12 isconnected with the resilient switch arm 10 so that, when the operationof the blower I4 creates a sufficient positive pressure to operate theheating system, the bellows 12 elongates and closes the switch 68, 10 toenergize the igniter 42.

A thermal switch 56, 51, in lseries with the igniter 42, is provided asshown and described in coonnection with Fig. 1.

When the valve 64 is ini the position shown, and the cabin supercharger6| -is initially operated, a strong current of air will pass from thesupercharger 6I and will flow through the casing 22, to the heating unitI0, through the air turbine I2 and through the conduit I6 to the cabin.This current of air will revolve the rotor 26 of the air turbine andthereby operate the blower I4, creating a. positive pressure at theoutlet of the blower I4 and thereby causing combustible mixture to ow tothe heating unit I0.

The rise in pressure at the outlet of the blower will cause the pressurewithin the bellows 12, in communication therewith, to rise and thebellows 'I2 will expand and will move the resilient switch arm 10 intoengagement with the contact 63 to close the igniter circuit. Currentthen flows from the grounded battery 60, through the thermal switch 61,56 and through the igniter 42 to the ground. This flow of current willheat the igniter 42 suillciently to ignite the combustible mixturewithin the combustion chamber housing 38 and will thereby establishcombustion. The heat of combustion will cause the temperature of thebi-metal 66 to rise, so that .the bi-metal 56 snaps away from thecontact 58 and thereby opens the ignition circuit and deenergizes theigniter 42. 'I'he hot gases of combustion from the combustion chamberhousing 36 pass through .the heat exchanger shell 44 and through anexhaust pipe 46, which discharges the products of combustion overboard.Heat conducted from the heat exchange shell 44 heats the longitudinalfins 49 which, in turn, heat the air flowing through the casing 22.

When the cabin supercharger 6I is operating, the operation of theheating system may be controlled solely by means of the valve 64. Thevalve 64 may 'be positioned so that all the air passing to the airplanecabin passes through the by-pass 62 and, therefore, the heating systemis not operated, or that none of the air passing to the cabin passesthrough the by-pass 62 and the lheating system is operated at itsmaximum capacity, or it may be placed in any desired intermediateposition so that the heating system operates at the desired fraction ofits capacity and the air passing to the cabin is heated to the desiredtemperature. It is to be noted that the amount of combustible mixtureburned in the heating system is controlled by the amount of air flowingpast the heating unit I0, so that the system cannot become overheated,and that the energization of the igniter t2 is controlled by theoperation of the heating system, so that the igniter 42 is energizedonly when necessary to ignite the fuel flowing to the heating unit andthere is no wastage of electric current.

While I have described my invention in connection with preferredembodiments thereof. it will =be apparent to those skilled in the artthat my invention may take various other forms without departing fromits underlying principles. I therefore wish to include within the scopeof the following claims all construction-s by which substantially theresults of my invention may be obtained by substantially the same orsimilar means. 1

I claim:

l, In a heating system for heating airplanes and the like, thecombination of an internal combustion heating unit for burning acombustible mixture of fuel and air, an air turbine, conduit means forconducting air past said heating. unit and through said turbine to aspace to be heated so that the current of air 'past said heating unitoperates said turbine, a carbureting device' for mixing fuel and air toform a combustible mixture, and means including a blower driven by saidair turbine for supplying combustible mixture lfrom said carburetingdevice to said heating unit.

2. In a heating system for heating airplanes and the like, incombination, an internal combustion heating' unit comprising acombustion chamber for burning a combustible mixture of fuel and air anda heat exchanger receiving the gases of combustion therefrom, a casingenclosing said heating unit, conduit means for conducting air from saidcasing to a space to be heated, a source of air under pressure forforcing air through said casing past said heat exchanger to the space tobe heated, an air current operatedmotor positioned in the path of ow ofair from said source through said casing to the space to be heated `andadapted to be actuated by the flow of air therethrough, a carburetor formixing fuel and air to form a combustible mixture, duct means forsupplying combustible mixture from said carburetor to said combustionchamber, a blower connected to said air motor for operation thereby tocause combustible mixture to flow through said duct means to saidcombustion chamber, and means for discharging the products of combustionfrom said heating unit.

3. In a heating system for heating airplanes and the like, incombination, an internal combustion heating unit comprising a combustionchamber for burning a combustible mixture of fuel and air, and a heatexchanger receiving the gases of combustion therefrom; a casingenclosing said heat exchanger, means for supplying air under pressure tosaid casing, conduit means for supplying air from said casing to a spaceto be heated, an air turbine located in the path of flow of air passingthrough said casing and adapted to be operated by said flow of air, acarbureting device for supplying combustible mixture to said combustionchamber, a blower for causing combustible mixture to flow from saidcarbureting device to said combustion chamber, a mechanical connectionfor operating said blower by said air turbine, and an air flowcontrolling valve located in the path of ow of the air passing throughsaid casing.

4. In an internal combustion heating system for heating airplanes andthe like, in combination, an internal combustion heating unit comprisinga combustion chamber for burning a combustible mixture of fuel and air,and a heat exchanger receiving the gases of combustion therefrom; anelectrical igniter for igniting the combustible mixture in saidcombustion chamber, a source of electrical energy, a switch in serieswith the source of electric current and the ignter, means actuated bythe current of air flowing past said heating unit for supplyingcombustible mixture under pressure to said combustion chamber, and anelement responsive to the pressure of the combustible mixture passing tosaid combustion chamber for closing said switch when said pressure is ata value high enough to cause combustible mixture to ilow to the heatingunit at a sufficient rate to maintain combustion.

5. In a heating system for heating airplanes and the like, incombination, an internal combustion heating unit, a source of air underpressure, conduit means for conducting air from said source past saidheating unit to a space to be heated, a valve positioned in said conduitmeans for controlling the ilow of air therethrough, a carbureting devicefor supplying a combustible mixture of fuel and air to said heatingunit, means responsive to the flow of air through said conduit means tosupply combustible mixture to said heating unit when and only when airflows through said conduit means, an electrically operated igniter forigniting the combustible mixture in said heating unit, a source ofelectric current for said igniter, a circuit for supplying current fromsaid source to said igniter, a switch in said circuit, and means forclosing said switch incldental to the opening oi' said valve and openingsaid switch incidental to the closing of said valve 6. In a heatingsystem for heating an airplane having a cabin supercharger and asupercharged cabin, in combination, an internal combustion heating unitfor burning a combustible mixture oi' fuel and air, a flrst conduit forsupplying air under pressure from the outlet of said cabin superchargerto said heating unit, a second conduit for conducting air from saidheating unit to the cabin of the airplane, an air turbine positioned inthe path of the ow of air through said heating unit and adapted to beactuated by said flow of air. a carbureting device for mixing fuel andair to form a combustible mixture, a duct for conducting combustiblemixture to said heating unit, a blower operated by said air turbine forcausing combustible mixture to ilow through said duct to said heatingunit, means by-passing said heating unit for conducting air directlyfrom the cabin supercharger to the cabin, and means for controlling therelative amounts of air ilow ing past said heating unit and through saidbypass means.

7. In a heating system for heating airplanes and the like, incombination, an internal combustion heating unit for burning acombustible mixture of fuel and air, a casing surrounding said heatingunit, a source of air under pressure, a ilrst conduit for conducting airfrom said source to said casing, a second conduit for conducting airfrom said casing to a space to be heated an air turbine located in thepath of flow of air from said source through said casing to the space tobe heated, a positive displacement blow er operated by said air turbineand having an inlet and an outlet, a carbureting device for mixing fueland air to form a combustible mixture, a duct for supplying air fromsaid first conduit to the said carburetor, a conduit for supplyingcombustible mixture from said carburetor to the inlet of said blower,and a duct for supplying combustible mixture from the outlet of saidblower to said heating unit.

8. In an internal combustion heating system for use in heating the cabinof an airplane having a cabin supercharger, in combination, an internalcombustion heating unit for burning a combustible mixture of fuel andair, a casing enclosing said heating unit, first conduit means forsupplying air from the outlet of the cabin supercharger to the inlet ofsaid casing, second conduit means for conducting air from the outlet ofsaid casing to the cabin of the airplane, an air turbine located in thepath of ilow of air flowing through said casing and adapted to be rotated thereby, a carbureting device for mixing fuel and air to form acombustible mixture means including a positive displacement bloweroperated by said air turbine for supplying combustible mixture from saidcarbureting device to said heating unit, a by-pass conduit forby-passing said heating unit and said air turbine for supplying airdirectly from the cabin supercharger to the airplane cabin, and valvemeans to control the relative amounts of air flowing through saidby-pass conduit and through said casing.

9. In a system for heating the cabin of an airplane, having a cabinsupercharger, and a, conduit for conveying air from said supercharger tothe cabin, a heater of the internal combustion type having a heatexchanger located in a section of said conduit for heating the airpassing therethrough, means forming a passageway by- .passing saidconduit section, damper means to determine the relative proportions ofthe air discharged by said supercharger and iiowing through saidpassageway and conduit section, and means responsive to the air flowthrough said conduit section for controlling the rate of production ofheat by said heater.

10. In a heating system for aircraft having a cabin supercharger, aconduit for conveying air from said supercharger to the cabin, saidconduit including a heater section, a heater of the internal combustiontype having a heat exchanger located in said conduit section to heat theair flowing therethrough, means forming a passageway by-passing saidconduit section, a turbine operated by the air flow through said conduitsection, means responsive to the speed of operation of said air turbineto determine the rate of heat production by said heater, and means forcontrolling the relative rates of air flow through said passageway andthrough said conduit section.

11. The combination set forth in claim 10, in which said means fordetermining the rate of production of heat by said heater includes afuel supply apparatus for said heater driven by said turbine.

12. In a heating system for aircraft, the combination of a conduit, anair ram for supplying air under pressure to said conduit, manuallyadjustable damper means controlling the rate of air fiow through saidconduit, an enclosed heater unit located in said conduit, an air turbinelocated in the path of now of air flowing through said conduit andadapted to be rotated thereby, and means operated by said turbine tosupply fuel to said heater.

13. The combination set forth in claim 12 in which said fuel supplymeans includes a positive displacement pump driven by said turbine andsupplying a combustible mixture of fuel and air to said heater unit.

14. In an aircraft heating system, the combination of an internalucombustion type heater having heat producing means and a heat exchanger,means for conveying air to be heated past said heat exchanger, pressuredifferential producing means for causing a flow of air through saidconveying means, motor means operated by the air flowing through saidconveying means, and means driven by said motor for supplying acombustible mixture to said heater.

15. In an aircraft heating system, the combination of a ram receivingatmospheric air under the dynamic pressure due to the motion of theaircraft through the atmosphere, a duct receiving air from said ram andfor conveying air to a space in the aircraft to be supplied with heatedair, a heater of the internal combustion type having a combustionchamber and having a heat exchanger located in said duct, and meansresponsive to the rate of fiow of air through said duct for supplying acombustible mixture to the combustion chamber of said heater at a ratewhich varies with said rate of air now.

16. In an aircraft heating system, the combination of a ram receivingatmospheric air under the dynamic pressure due tov the motion of theaircraft through the atmosphere, a duct receiving air from said ram andfor conveying air to a space in the aircraft to be supplied with heatedair, a heater of the internal combustion type having a combustionchamber and having a heat exchanger located in said duct, and means forsupplying fuel to the combustion chamber at a rate varying with the rateof flow of air through said duct.

1'7. In an aircraft heating system, the combination of an internalcombustion type heater having a heat exchanger, means for conveying airto be heated past said heat exchanger, motor means operated by airiiowing past said heat exchanger, means driven by said motor means forsupplying a combustible mixture to said heater, and means to regulatethe iiow of combustible mixture to said heater by controlling.

the rate of iiow of air past said heat exchanger.

18. In an aircraft heating system, the combination of an internalcombustion type heater having a heat exchanger, means for conveying airto be heated past said heat exchanger, motor means operated by airflowing past said heat exchanger, means driven by said motor means forsupplying a combustible mixture to said heater, an electric igniter, anenergizing circuit therefor, and common means for controlling saidenergizing circuit and the iiow of air past said heat exchanger.

19. In an aircraft heating system, the cornbination of an internalcombustion type heater having a heat exchanger, means for conveying airto be heated past said heat exchanger, motor means operated by airflowing past said heat exchanger, means driven by said motor means forsupplying a combustible mixture to said heater, means providingv apassageway for by-passing air around said heat exchanger, and means forregulating the relative rates of air flow through said by-passpassageway and past said heat exchanger.

20. In an aircraft heating system, the combination of an internalcombustion type heater having a heat exchanger, means for conveying airto be heated past said heat exchanger, motor means operated by airflowing past said heat exchanger, means driven by said motor means forsupplying a combustible mixture to said heater, and means to preventeffective operation of said heater when said means for supplying thecombustible mixture to said heater is delivering such mixture at lessthan a predetermined pressure.

21. In an aircraft heating system, the combination of an internalcombustion type heater having a heat exchanger, means for conveying airto be heated past said heat exchanger, motor means operated by airflowing past said heat exchanger, and means driven by said motor meansfor supplying a combustible mixture to said heater, said last namedmeans including a carburetor and a positivedisplacement air pump drivenby said motor means for supplying air to said carburetor.

HENRY J. DE N. MCCOLLUM.

